A major, critical bug and possible security threat has been discovered in Ubuntu Breezy. Apparently, the 'root' password (not actually the root password because Ubuntu uses sudo) gets written into the installer's log files in clear text, and can be read by any account on the Ubuntu machine. The bug was first discovered and reproduced on the Ubuntu forums. The bug does not seem to affect Dapper, however, users upgrading from Breezy to Dapper might still be at risk because the log files are not modified. Update: Bug is fixed. Please upgrade.

So you get Joe User who has managed to happily install Ubuntu, and he tells his OS X/Windows-using friend how great and secure it is. Said friend knows about the log file, finds it, gets root on Joe's box. Joe is not happy, and realizes that the Linux zealots on some forum or other were just spewing bullshit.

Some friend. That makes no sense at all. Put me in the room with anyone's desktop Wintel running Linux, and I can hax0r it with a liveCD and chroot. Even change the root password. If we're talking about a system you could just reach around and unplug or open up and remove the hard drive from, nothing you can do in software really counts as breaking in. This "exploit" affects basically two people: paranoid parents and people with untrusted guest accounts.